The application of enamel by electrodip enamelling (electrophoresis, the so called ETE process) is known. Production plants of various types of construction, primarily for domestic appliances, have been described in the literature (see Warnke, F. Kaup, Maschinenmarkt 80 (1974), page 4; or H. Hoffman, Mitteilungen des VDEFa 24 (1981), page 107; Warnke, Kaup, Mitteilungen des VDEFa 22 (1974), page 49; Hoffmann, Mitteilungen des VDEFa 26 (1978), page 91, van der Vliet, Mitteilungen des VDEFa 25 (1977), page 49). Electrodip enamelling is generally confined to the application of a single layer as it requires a conductive, metallic base.
Once an enamelling has been stoved, it can no longer be electrophoretically coated with additional layers. In the process of application, the deposited layer solidifies due to electroosmosis so that loosely adhering particles may subsequently be washed off. Under certain conditions (sufficiently firm deposition; suitable adjustment of the products as regards their melting properties and interface reactions) it is even possible to apply an additional layer to this base. If a suitable combination of products is used and both systems deposit well by electrodip coating, this second layer may also be deposited electrophoretically.
In enamelling processes which entail the application of a base layer followed by a top layer of enamel and in which the two layers are stoved together but a process of application other than electrophoresis is used, e.g. powder electrostatic application (PUESTA). It is also known that the base enamels are required to be easily flowing and of low viscosity at the appropriate stoving temperature (W. Joseph; Mitteilungen VDEFa 1981 page 159).
When such types of base enamel are used for electrophoretic application, the process becomes very trouble prone since enamelling faults frequently occur, e.g. surface faults, due to electrolytically produced blisters.